Slide valves comprising a multi-part housing having a passage opening and comprising two slider plates, parallel to one another, moveable at right angles to the passage opening are known. The two slider plates are connected to one another rigidly and can be moved from an open position into a closed position tightly blocking the passage opening by means of a common drive mechanism. With these slide valves it may be the case that over time only one of the two slider plates rests tightly against the corresponding counter-surface of the housing in the closed position, and so performs the blocking function by itself.